Hot melt adhesives are used in the automated packaging industry for sealing cases and cartons. Usually the viscous melted adhesive is extruded under high pressure through a nozzle having a small volume capacity to eliminate problems of tailing, drooling and stringing between applications. A typical hot melt adhesive extruder of the prior art, employing pressure to supply the adhesive, is that of U.S. Pat. No. 3,585,361. The use of high pressure to force the adhesive through the smaller capacity nozzle orifices presents an occupational risk to workers, as well as the expense of pressure resistant hoses, fittings and couplings which may be eliminated if nozzle performance, using low pressure applicating equipment, could equal that produced with the high pressure equipment. The use of larger orifices on the nozzles for lower pressure equipment would eliminate the problems of clogging with char particles from degraded adhesive found in the capillary nozzles, which necessitates use of filters with the high pressure apparatus. However, the larger diameter orifices may cause problems of drooling from the nozzle tips between applications because of the large volume of adhesive material past the cut-off valve. Decreasing the size of the bore of the passageway supplying adhesive to the nozzle tip would interfere with adequate adhesive flow under low pressure conditions. Prior art devices have employed the use of minimum reservoir spaces and small ports, in which capillary action causes the adhesive to return to a distributing passageway from the discharge port when the valve is closed, as in U.S. Pat. No. 3,126,574. However, this type of port sometimes delivers blobs of glue rather than continuous strips. In U.S. Pat. No. 3,078,824, the nozzle orifice itself is closed by a valve to minimize dripping from the nozzle when delivery of the adhesive is stopped. In. U.S. Pat. No. 2,100,342, the nozzle has a resilient tip portion having an open-ended compartment in the flat tip, into which glue is delivered through minute passages from a reservoir in the body of the nozzle. Any adhesive left in the open compartment, after delivery of the adhesive to the nozzle is stopped, is removed from the open-ended compartment on the tip by allowing it to harden and then distorting the flexible tip end thereby breaking away the hardened adhesive.
None of these nozzles taught by the prior art are useful for the precise application of hot melt adhesive in strip formation from a multi-orifice nozzle assembly to carton or cases under automated assembly line conditions.
An object of the invention was to devise a multi-orifice nozzle assembly that could be used with low pressure hot melt adhesive dispensers and that would maintain clean nozzle cut-off between applications without drips, drools, or leaks from the nozzle tip.